The preferred embodiment concerns methods and devices for processing a print data stream that serves to generate print images with at least two primary colors with the aid of a high-capacity printing system.
Multicolor print images to be output with the aid of a high-capacity printer (such as, for example, photographs, color graphics or multicolor text) are described with the aid of print and/or image data contained in a print data stream. The print data and/or image data specify color separations of typical primary colors that are used by high-capacity printers for image generation. Such high-capacity printers have the primary colors cyan, magenta, yellow, black corresponding to the CMYK color model as well as (possibly) one or more special colors such as, for example, the Océ Custom Tone colors from the applicant. Various high-capacity printers are described in the publication “The World of Printers, Technologies of Océ Printing Systems”, Dr. Gerd Goldmann (Editor), Océ Printing Systems GmbH, Poing, 7th Edition, (2002). In particular, offset printing and digital printing technologies are described on pages 249-286. Various digital color printing systems are described on pages 287-325; the foundations of multicolor printing are described on pages 233-248; and the foundations of digital image processing are described on pages 209-232. Principles of highlight color printing are also described on pages 246-248.
Trapping generally means an overfilling of individual regions to be inked with the aid of a primary color, and thus an overfilling of the regions of individual color separations to be inked. Given imprecise positioning of two color separations to be transfer-printed next to one another, un-inked regions can arise at the boundary line of two adjoining regions to be inked, via which un-inked regions the color of the substrate material is visible in the finished print image. In order to avoid this, the region to be inked with the aid of individual primary colors is enlarged with the aid of a trapping method so that these regions are overfilled. Given an optimal positioning of multiple color separations atop one another (which cannot be implemented in practice), uniform overlaps would be generated by the trapping in the border regions of adjoining regions of different color separations to be inked. In practice, different overlap widths are achieved due to the positioning of the individual color separations, which is not 100% precise. Depending on the requirement (i.e. depending on the imprecision of a printer in the positioning of individual color separations atop one another), the degree of the enlargement of the regions of the individual color separations to be inked (i.e. the degree of the overfill) that is to be implemented is selected such that no regions in the print image are to be expected that are not inked or are only insufficiently inked in a region in which inked regions of different color separations adjoin one another.
A method and a printing system for trapping image data are known from the international patent application PCT/EP 2005/057147 (not previously published; internal file number of the applicant is 2004-1204P).
Methods and systems for trapping raster images along horizontal, vertical or diagonal directions that use only edges of diagonally adjacent pixels for trapping are known from the document U.S. Pat. No. 6,377,711 B1.
A method and a device for automated acceptance and relaying of document processing jobs are known from the document WO 03/065197 A2. In particular, a folder is thereby used in order to cache the print data of a print job in this folder. The print data stored in this folder are then processed further. For example, the document management system “Prisma Production” from Océ Printing Systems (which is likewise described in the aforementioned publication “World of Printers, Technologies of Océ Printing Systems”) has such a functionality. High-capacity printing systems (whose printing speed is, for instance, 40 pages up to over 1000 pages of DIN A4 per minute) advantageously process print data streams such as, for example, a print data stream based on a Page Command Language (PCL), an Advanced Function Presentation (AFP) print data stream or a printer-side Intelligent Printer Data Stream (IPDS) corresponding to the AFP print data stream. The AFP data format of an AFP data stream has been developed by the International Business Machines Corp. (IBM). An additional print data stream standard distributed in high-capacity printers is the Line Condition Data Stream (LCDS) of Xerox Corp.
Details of the document data stream AFP™ are described in publication Nr. F-544-3884-01, published by International Business Machines Corp. (IBM) with the title “AFP Programming Guide and Line Data Reference”. The document data stream AFP was developed further into the document data stream MO:DCA™, which is described in the IBM publication SC31-6802-06 (January 2004) with the title “Mixed Object Document Content Architecture Reference”, for example. Details of this data stream are also described in U.S. Pat. No. 5,768,488.
AFP/MO:DCA data streams are frequently converted into data streams of the Intelligent Printer Data Stream™ (IPDS™) in the course of print production jobs. Details regarding IPDS data streams are described in the IBM document Nr. S544-3417-06, “Intelligent Printer Data Stream Reference”, 7th Edition (November 2002), for example.
High-capacity printers implement a raster image process—advantageously with a separate raster image processor (RIP)—to generate raster images of individual color separations. This raster image processor can be realized as hardware or software. An image process integrated into an output management system is known from the document WO 02/093353 A1, with the aid of which output management system raster images can already be generated in the print preparation in the same way as with the aid of a raster image processor arranged in the printer, in order to check the individual color separations.
Methods and devices for electronic trapping of raster images are known from the documents US 2005/0219631 A1, U.S. Pat. No. 6,594,034 B1, U.S. Pat. No. 5,581,667 A and EP 0 833 216 A2. A trapping of print images described by Postscript or another page description language (PDL) is known from the document WO 95/20796 and U.S. Pat. No. 5,667,543 A. Additional methods for trapping are known from the documents DE 199 12 511 A1, U.S. Pat. No. 6,813,042 B2, EP 0 929 189 A2, JP 2004-262011A and U.S. Pat. No. 6,441,914 B1. The content (in particular the image processing methods and image generation methods known from these documents) are herewith incorporated by reference into the present specification.
The aforementioned publications or documents are herewith incorporated by reference into the present specification, and the methods, systems and measures described there can be applied in connection with the present preferred embodiment.
The methods known from the prior art to improve the image quality of an image to be output (in particular the trapping methods known from the prior art) are not suitable for use in connection with AFP, LCDS and PCL print data streams since these print data streams do not support the transfer of trapping information. It is also desirable to adapt a method for image processing that is to be implemented more flexibly to the requirements of a selected printer, and to be able to also modify this adaptation at a later point in time if necessary. A trapping is thus presently not possible in the known and further print data streams for high-capacity printing systems when print-prepared print data streams are already present. Un-inked regions can thus not be safely avoided due to imprecisions in the positioning of the individual color separations to be generated on a substrate material to be printed or an intermediate image carrier in known high-capacity printers. These un-inked regions are disruptively visible in the finished print image generated on the substrate material.
Printing systems are known in which a trapping for Postscript and PDF print data streams is implemented in the controller of the printed. However, such a trapping in real time is possible only with significant additional expenditure in high-capacity printing systems.